Gmail is popular but in the grand scheme of things it’s not that popular for email. I’m sure that most people get most of their utility from email from their corporate email. Their personal email is mostly used for distant relationship type communications. Most personal interactions these days happen via messaging and social media. AKA “Email is for old people”.

Also, a lot of computer use is via mobile these days and I doubt too many people are using the web interface on mobile for gmail.

To say that Gmail had much to do with Google’s growth considering that there was only a relatively small Window that email was the most popular form of personal (not corporate communication and spam) and that was over ten years ago before mobile started taking over doesn’t really have any basis in today’s reality.